Gyro-stabilized sextant



0. E. ESVAL ETAL GYRO-S'I'ABILIZED SEXTANT Filed Sept. 26, 1941 Nov. 20, 1945.

ZTE= Z INVENTORS, ORLAND E. EsvAL Ma WRIGLE THEIR ATTORNEY.

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GYROS TAB ILI ZED S EXTANT Filed Sept. 26 1941 4 Sheets-Sheet 2 INVENTORS, ORLAND E. ESVAL WALTER WRIGLEY,

Nov. 2@, 3945. o. E. ESVAL ETAL GYRO-STABILIZED SEXTANT Filed Sept. 26, 1941 4 Sheets-Sheet 3 Y v M m Em Y O .R E TEW N we m vN NAE M m 4 Sheets-Sheet 4 m a m w w 0. E. ESVAL ET AL GYRO-STABILIZED SEXTANT Filed Sept. 26 1941 H9 I r em Nov. 20, 1945.

I04 IOI 7 I I I I INVENTbRS, ORLAND E.EsvAl WALTER WRIGLEY,

The pivot axis of bushings 1 and II is placed exactly along the transverse or athwartship axis of the craft. By means of slot, I1 and handwh'eel 25, the orientation of the optical axis 26 of the instrument may be compensated for any normal or fixed trim of the craft by shifting supporting case 9 relative to spider 3 until the optical axis is truly vertical, whereupon h'andwheel is tightened to maintain this trim adjustment. The conditions which indicate when the optical axis 26 is actually vertical are described below.

Since the instrument is intended for use in pressure-type aircraft cabins, supporting case 9 is joined to wall I of the craft by flexible membranes 21, which maintain an air-tight condition within the cabin but still permit slight relative motion between supporting case 9 and wall I in order to allow the trim adjustment just described.

The instrument proper is rotatably supported within outer supporting casing 9. As shown best in Fig. 1, the instrument comprises a tube 29 concentrically positioned within case 9 and supported therefrom as by bearings 3| which permit tube 29 to rotate within supporting case 9. Tube 29 carries at its upper end the optical head 33 which projects outside wall I. At its lower end, tube 29 is connected to a platform 35. Lower casing 31 is supported from platform 35 and carries most of the remaining elements of the instrument.

In order to maintain an air-tight condition, two cylindrical sleeves I2, I4 are fastened to the outer surface of tube 29, and these sleeves I2, I4 and the inner surface of case 9 are machined to fit very accurately so as to maintain a practically air-tight running fit. A thin, practically capillar film of lubricant is placed between these closely fitting surfaces. The large film area and close clearance act to preserve this air seal. In addition, the annular groove I0 between sleeves I2 and I4 is filled with oil or other lubricant, inserted through hollow bushing I I with which this annular space I0 connects, thereby further improving the air seal.

The lower casing 31, tube 29 and head 33 are rotated in azimuth from azimuth control wheel 39 (Figs. 2 and 5). This wheel 39 is connected by detachable bevel gears 4|, 43 to shaft 45, which carries a bevel gear 41 at its upper end. Bevel gear 01 mates with bevel gear 49 to turn cross shaft 5|, also shown in Fig. 1. Cross shaft 5| has bevel gear 53 attached to its other end, this bevel gear 53 mating with bevel gear 55 to turn pinion 51. Case 9 has an annular ring gear 59 fastened to or formed integrally with itself, and this ring gear 59 meshes with pinion 51. Accordingly, rotation of azimuth control wheel 39 will cause pinion 51 to walk around ring gear 59, which is fixed relative to the craft. Pinion 51 passes through bearing BI in platform 35 and accordingly carries that platform, and hence the entire instrument, around with itself.

Supporting case 9 may have a scale 63 fastened to it, which cooperates with an index on platform 35 to give azimuth indications. Also, a Selsyn transmitter 65 may be connected to shaft as by gearing 01 to transmit azimuth indications to a remote point.

Sighting head 33 is supported on a platform 69 fastened to or integral withthe upper part of tube 29. This platform 59 supports a hood 1| having a window 13 for viewing the distant object to be sighted. Window 13 preferably contains means for mimimizing frosting thereof, such as current carrying wires. Alternatively, it may be formed of a material which absorbs light radiation and converts it into heat. The image of the distant object is picked up through window 13 by entrance prism 15, which is formed as a double prism having a reflecting boundary 18 between the two sections thereof. The image is reflected by prism 15 through lenses 11, 19, 8| forming the main optical system of the sextant, and then through reflex mirror 83, where the object image is superposed on the reticle image and trim image, as will be later described. The combined image is projected through objective and reflected by mirror 81 through field lens 89 and eyepiece 9| to be there viewed by the operator,

Referring now more particularly to Figs. 6 and 7, the reticle image is obtained by projecting a light source 93, preferably formed by an incandescent lamp, through a condensing lens onto a flashed opal 91 which collects light from source 93 and acts as a secondary light source. Light from flashed opal 91 is collimated by collimating lens 99 and projected in parallel rays through a blocking screen |0I having crossed slits I02, I03 through which the light ray from secondary source 91 pass onto a ground glass screen I04 in the form of a cross of light. The image of this light cross is projected by lenses I08, I01, I08, mirror I09 and lens IIO onto reflex mirror 83 to be superposed on the object image received from entrance prism 15.

Ground glass screen I04 may have drawn on it some distinctive pattern, such as the outline image of an airplane, which we shall call the trim image because of its function, as will be later described. This trim image and the reticle light cross are projected together by lens system I06, I01, I08, I09, IIO to be superposed on the object image at reflex mirror 83. The trim image may be drawn with fluorescent material which becomes visible only when irradiated by ultraviolet light. In this way the intensity of the trim image can be controlled by controlling the amount of ultra-violet radiation from a source not shown.

Primary light source 93 and condenser lens 95 are fixed to housing 31, as is most clearly shown in Fig. 6. However, the light cross projected through shield I0| is stabilized by gyro I so as a to remain always in a horizontal plane. Thus, referring to Figs. 6 and 7, gyro rotor housing H2 is mounted in gimbal ring 3 for rotation about a horizontal axis, and ring 3 is pivotally mounted on main housing 31, one pivot being shown as II4. Pivot H4 is extended into forked member IIS, inside which housing II1, which carries secondary light source 91, collimator 99 and light shield IOI, is pivotally mounted about pivots H8. The pivot axis 8 is made to pass through the center of secondary light source 91, which i also made coaxial with pivot II4. In this way, secondary light source 91 is substantially immobile with respect to main housing 31, merely rotating about its center, which is fixed with respect to housing 31. The upper part of housing 1 is connected to the rotor housing 2 by a link I I9 pivotally fastened to the rotor housing H2 at |2I and to housing 1 at I22. In this manner, housing I I1 is always kept parallel to the spin axis of gyro III, which is kept vertical by any well known gyro erecting means. The light cross formed by shield |0I is thereby maintained stabilized in a horizontal plane at all times.

The time image, as described above, is placed on ground glas screen I04. It may be drawn in shape of an airplane I05 and oriented so as to indicate the actual craft heading. Since the entire housing 31 rotates during operation of the device, it is necessary to provide some means for maintaining the trim image fixedly oriented with respect to the craft. This is done by rotating ground glass screen I 04 in a reverse direction by the same amount that housing 31 is rotated forward. The screen I Ill-is mounted in a holder I 23 provided with gear teeth I 24. Holder I23 rotates about its supporting tube I26. As shown schematically in Fig. 5, screen I is driven from azimuth control 39 by means of shaft I29 connected to gearing 61, and gears 828 and ME. Screen 504 thereby rotates equally and oppositely to the rotation of housing 31, whereby the trim image remains fixed with respect to the craft.

It is apparent that the optical axis of the reticle projecting system is maintained vertical at all times by means of its gyro stabilization. Accordingly, the inclination of the instrument optical ems can be determined by comparison with the reticle system axis. For proper adjustment, the instrument optical axis should be vertical when the craft is flying under normal conditions and with normal trim. To obtain this adjustment, the trim adjustment described above is varied until the center of the reticle image falls on the center of the trim image. Once this adjustment is made, it is left set until the normal trim of the ship is changed, whereupon the sextant trim adjustment must be reset.

The system just described also serves to indicate the instantaneous attitude of the craft. When the reticle image center and the trim image center coincide, and the trim adjustment has been made, the operator will know that the craft is flying correctly, with normal trim. When the reticle image center departs from the trim image center, the operator is thereby warned that the craft has deviated from its normal attitude. The departure of the two images will indicate, by its amount and direction, the change in attitude of the craft. or attitude indicator is provided.

The control of the line of sight in azimuth has already been described, The control in elevation is secured by rotating entrance prism 55 about a horizontal axis. an elevation control knob i3I rotates a shaft i552 through selectively engageable reduction gearing E33 and bevel gearing 35. Shaft it? is connected to a bevel gear E35 which meshes with a second bevel gear its which turns shaft l3? (see Mg. 4). A rotation counter I238 is rotated by shaft it? through speed-change gearing 5&9 and bevel gearing iGE. Also coupled to shaft til, as by bevel gearing H22 and off-setting gears ass, is a drive shaft Edd having a'worrn ME connected thereto. Engaging with worm M8 is a worm-wheel sector E li which is secured to axis Mall of prism 15. Asshown best in Figs. 2 and 8,

prism i5 is mounted for rotation about horizontally disposed pivots M9 supported in a bracket (5% supported on platform 59. It is clear, therefore, that rotation of elevation control I3! will produce corresponding rotation of prism E5 to change the elevation of the line of sight, which is indicated by the reading of counter E35 suitably calibrated for this purpose.

A Selsyn transmitter 552 (Fig. 2) may be coupled to shaft 632 as by gearing H5 3 to transmit the angle of elevation to a remote point. By these transmitters lot and 85, the exact position of the sighted object can be transmitted to any desired location. Thus, the present device may be used to locate targets for gun fire, and the remote indications may serve to indicate the target position to a fire control operator. In addition, the trim indicator discussed above will enable the determination of a proper'firing time at which the attitude of the craft will not interfere with the accuracy of fire.

Also incorporated in the elevation control is a safety device to prevent injury to the prism. A screw thread I 56 is formed on shaft I32, along which a nut I51 travels. Stops I58 prevent excess travel of nut I51 and hence of prism 15, thereby avoiding injurious contact between prism and its mount.

A further feature of the present device resides in the provision of filters insertable into the opihus an instantaneous trim tical system. Referring to Figs. 1, 2 and 3, three filter holders IGI, I62, I63 are shown. Each is fastened to e. pinion I84, I65, E66 pivoted about a common axis I61. Each of these pinions I64, I65, IE6 is driven from a corresponding one of handles I58, I69, 510 throu h suitable shafts and soaring, as shown. Thus each of handles I 88, E39, I76 serves to swing its corresponding filter into or out of the optical system. A spring detent and notch III is used to keep each filter in proper position.

The lowermost filter may be formed of dark glass for viewing the sun. The upper pair of filters may be formed of light polarizing material, whereby relative rotation of one filter with respect to the other may control the light intensity passing into the optical system. For this purpose, the uppermost filter H2 is placed loosely in its holder idl and has a ring gear I13 formed as its outer periphery. Ring gear I13 meshes with idlerpinion lid and gear I16, which is driven from control wheel ill by suitable gearing and shafts. Hence, control wheel il'l adjusts the light in tensity of the sighted object as viewed by the observer.

Fig. 9 shows a modification of the reticle projection system shown in Fig. 6. In Fig. 9, primary light source 93 is mounted at the pivot of housing ill in place of the secondary light source 91 of Fig. 6. Light source 93 is projected directly upon ground glass EM through the crossed slots in blocking screen I (it by means of projecting lens 99, as in Fig. 6. Lens 99 may be adjusted as by slots I19 and screws M8 for proper focus and projection. Theoperation of this modification is otherwise exactly the same as that of Fig. 6.

Fig. 10 shows a further modification of a portion of Fig. 6. Here light from secondary light source or flashed opal at is focussed by len -system 99 on an added lens IBE, through the crossed slits of blocking screen EM. Lens EBE serves to focus the image of the lighted crossed slits onto ground glass it, rather than merely projecting light through the slits, as in Figs. 6 and 7. It is clear that here, too, flashed opal 9'? may be replaced by primary light source 93, as in Fig. 9.

As many changes could be made in the above construction and many apparently widely differ-' ent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

I. In a sextant having an optical system including a combining mirror through which distant objects may be viewed, a gyroscope having a casing, a gimbal ring supporting the gyroscope and casing, a. tubular member, means for maintaining the member parallel with the spin axis of the gyroscope, comprising means for supporting 'the member for rotation about two intersecting axes, a connection between the member and a pivot of the gimbal ring for turning the member about one of the axes, a connection pivoted to the member and to the gyroscope casing for turning the member about the other of the axes, means for illuminating the interior of the member disposed substantially at the intersection of the axes, a reticle disposed within the member illuminated by said means, optical means for projecting rays of light from said reticle onto said mirror to serve as a stabilized reference for the distant objects viewed through the optical system.

2. A sextant according to claim 1, wherein the means for illuminating the interior of the tube comprises a light bulb.

3. A sextant according to claim 1, wherein the means for illuminating the tube comprises a flashed opal, means for illuminating the opal comprising a light bulb disposed beyond the tube at a fixed distance from the intersection of the axes. the arrangement being such that the opal due to its location at the intersection of said axes receives uniform illumination irrespective of relative movement of the axis of the gyroscope and the light bulb.

4. In an optical system including a combining mirror for a sextant or the like foruse on unstable craft, a stabilized reticle arrangement comprising a tubular member, a gyroscope enclosed in a casing, a gimbal ring mounting therefor, means for maintainin the member in predetermined alignment with the spin axis of the gyroscope comprising means for supporting the member for rotation about two intersecting axes, a connection between the member and a pivot of the gimbal ring for turning the member about one of the axes, a connection pivoted to the member and to the gyroscope casing for turning the member about the other of the axes, means for illuminating the interior of the tubular member supported substantially at the intersection of said axes, a reticle disposed in the tube so as to be illuminated by said means, optical means for projecting a beam of light from said illuminating means shaped by the reticle onto the combining glass as a reference for objects viewed through the optical system, means normally fixed with respect to the craft for projecting onto the mirror an image indicative of the relative position of the craft with respect to the beam of light from the reticle and the objects viewed through the optical system.

5. A sextant comprising a vertical telescope tube mounted for rotation about its longitudinal axis and having an optical system including a transparent mirror through which celestial objects may be viewed, a reticle, a source of light for illuminating the reticle, a common movable support to which the reticle and source are fixed in spaced relation, a vertical gyroscope, coupling means for the support and gyroscope for maintaining the support parallel with the spin axes of the gyroscope, a rotary translucent screen provided with a device for indicating the angular position to which the telescope tube has been rotated with respect to an axis of a supporting craft, the support for the reticle being so disposed that light rays from the reticle project an image thereof on the translucent screen, optical means for projecting an image of the screen onto the combining mirror whereby images of the reticle and indicating device may be observed to be used as references for the images of the celestial objects viewed therethrough, a gear drive coupling the telescope tube with the screen for maintaining "the screen and indicating device thereon in predetermined position with respect to an axis of the supporting craft irrespective of the rotary movement of the telescope tube.

6. A sextant comprising a vertical telescope tube mounted for rotation about its longitudinal axis and having an optical system including a transparent mirror through which celestial ob jects may be viewed, a rotary screen provided with an indicating device adapted to be set in predetermined relation to an axis of a supporting craft, means for projecting an image of the screen onto the transparent mirror whereby the indicating device may be observed with the objects viewed through the optical system, gear means coupling the screen and telescope tube for maintaining'the screen in predetermined position irrespective of the rotary movement of the telescope tube whereby the indicating device serves as a reference from which the extent of the rotation of the tube may be observed while viewin celestial objects.

7. A sextant according to claim 6, in which a further reference is provided comprising a stabilized reticle, and means for projecting an image of the reticle together with that of the screen onto the transparent mirror.

ORLAND E. ESVAL. WALTER WRIGLEY. 

